Resettable fuse used in LED power protection circuit protection
1. Transient voltage system diode (TVS for short) Transient voltage system diode is a kind of diode-based high-efficiency maintenance device. When its electrodes are subjected to reverse transient high-energy shocks, the high resistance between the electrodes can be immediately reduced to low resistance at a speed of minus 12 to the power of 10 seconds. Receiving surge power of up to several kilowatts, the voltage between the electrodes is clamped to a predetermined voltage value, which effectively maintains the fine components in the electronic circuit. Transient voltage control diodes have the advantages of fast response time, large transient power, low leakage current, good breakdown voltage bias consistency, easy clamping voltage control, no damage limit, and small size.
However, in practical applications, it is not easy to find a TVS device that satisfies the required voltage value. The damage of the LED light source is mainly caused by the overheating of the current inside the Ambassador chip. TVS can only detect overvoltage and overcurrent. It is difficult to grasp the proper voltage maintenance point, such a device cannot be produced and it is difficult to use it in practice.
2. Fuses (tubes) are used in maintenance LED circuits because fuses are disposable. And the response speed is slow, the result is poor, and the use is cumbersome, so the fuse is not suitable for LED lamp products. Because LED lights are currently the first glorious project and lighting project in the city. It requires LED maintenance circuits to be demanding: When the normal operating current is exceeded, maintenance can be started immediately, so that the power supply path of the LED is disconnected, so that both the LED and the power supply can be maintained. After the entire lamp is normal, the power can be actively restored without affecting the LED task. The circuit cannot be too complicated, the volume cannot be too large, and the cost is even lower. So using the fuse method is very hard to accomplish.
3. Choosing a self-recovery fuse, also known as polymer polymer positive temperature thermistor PTC, is composed of polymer and conductive particles. After extraordinary processing, the conductive particles form a chain-like conductive path in the polymer. When the normal task current flows (or the component is at the normal temperature), the PTC resettable fuse is in a low resistance form; When an abnormal overcurrent flows in the circuit (or the temperature rises), the heat generated by the large current (or the temperature rises) makes the polymer expand rapidly. In this way, the conductive path composed of conductive particles is cut off, and the PTC resettable fuse has a high resistance form; When the overcurrent (overtemperature condition) in the circuit disappears, the polymer cools and the volume returns to normal. The conductive particles in the medium form a conductive path again, and the PTC resettable fuse has an initial low resistance form. In the normal task form, the fever of the self-recovery fuse is very small, and in the abnormal task form, the fever has a very high resistance. It also limits the current passing through it, and then has a maintenance effect. In the detailed circuit, you can choose:
①Bypass maintenance. Ordinary LED lights are divided into many branches. We can add a PTC component to the front of each manifold for maintenance. The benefits of this method are high accuracy and reliable maintenance.
② Overall maintenance. Add a PTC element in front of all light beads to maintain the entire lamp. The benefit of this method is simplicity and it does not take up volume. As far as the civil products are concerned, the consequences of this kind of maintenance in practice are still impressive.
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